Alumina-cobalt-gold composition



Q No Drawings :Filed Feb. 25, 19'64',"Ser.-No.

, as .the 'principa ting micron.

step'is used) isthen LU INA-Co r-GQL .COMBOSIIION a Ralph,P Leveyp Jrgioak Ridg'c flTennl, .assignor to the UnitedStates of-Americn as represented by the United .StatesAtomic'Energy Commission 347,318

- '10 Claims.' 75- 206) United States Patent Oil ice I a Patented; Sept. 28, 1965 keptbelow about .20". C. per hour, and preferably 5 to f C. per hour inorder to prevent bubble formation.

Having thus described my invention the-following examples are given to illustrate it-in more detail. Examples I and II show a method of making articles having my preferred composition and .give the. results of physical tests on these articles; Examples III-VII-give the results My invention Lrelates to materials containing alumina I l consti'tuent and particularly-to such ma 'terials havingfaihigh compressive strength? Materials which are exceptionally hard and which havea high --c ompressivc'strength areuseful as elements in highpressure, high {temperature equipment and as cuttips for mach'inetools. Harder, strongerimater'ials' than'those .prcsently available-are desirable.

Iha've discovered that a composition consisting essene gold. is 310212 percent-of the totalweight composition is unexpectedlyhard and has-exceptionally I high c'ompres'swei' strength" 'Toollups made from com" sel. .Th epressure within the vesselwas raised to about 200,000-pounds per square'inch and held at that level' positions in this, rangeare .abieffto sustain heavier cuts than the best'cornmercially available "oxide or. carbide tools-,'- and compressive testing indicates the material is hot: only stronger; butis more ductile than other-oxides tially of 80 to"97'-per.cent alumina and 3 to ZO-percent of a,. mi;xtur -.of,the-rnetals cobalt and gold, ,whereinthe vieight ,of the metal co'mponents, has excellent "high pres'sureQhigH- ofcomparable tests made on other compositions; and Examples VIII-XII give the results of cutting tests made using commercially-available compositions for tooltips.

EXAMPLE If:

YAlumina powder having an average particle diameter of about 0.05 micron waswet-milled with 5-40 micron cobalt powder and- 5-30 micron gold powder in a 1:1 water-alcohol mixture for 150 hours. The volume ratio of powder to liquid was 1:3, The powder mixture con: tained 96.7 weight percent A1 0 3.0 percent Co and 0.3 The ball mill and the balls were .of'high percent Ali. density Alg0 1 5 The milled powders werevacuurn dried at 300 F.,

the dried powder was .tamped into a'rubber mold, and,

the filled mold was evacuated, sealed and immersed in a light mineral oil in a piston-cylinder. type pressure ves- The resulting pressed mixture had about 1 atmosphere. The temperature was raised-at 20 C. per

- Materials of this'cdmposition.containing'less than about 95;percent'a'luminaare softer than the materials containing9-5" to' 91 .percent alumina, yet havehigh strength at 'elevate'd temperatures, and are useful as structural materialswhere high temperature strength is needed.

Articleshaving this icompositionmay be made by first mixing together alumina powder, cobalt powder, and

powder 'should be as fine as possible, and the preferred powders have an average particle diameter of 0.05 to 0.5

While the cobalt and gold powdersmay have an averag'e'particle diameter as great, as :micron s, the

preferred powder has .an average particle diameterof 1' to. Smicrons." a

The powders may be mixedby any conventional means which will;make ar-homogeneous mass of the powders "without adding impurities. f p The mixed powders'are then formed into a body. This may bedone' by -merely placing the powder mixture within a mold and pressing it until the powder mass reltains the configurationjofithe mold upon separation therefrom. In -the preferred method of forming a body from powders, the formed shape is subjected to a high pressure,

at least about-100,000 pounds-per square inch' and preferably 125,000. to 200,000 pounds per square inch. Al-

thougharticles; made: from my composition will have excellent mechanicalproperties even if the powder mass Theshaped mass'of hardness desirable for some uses without such a step.

phere.

-sin'te.ling temperature of about 1450 to 1550 C. is

preferred. In. sintering, the temperature rise must be 40 gold powder'in the; proper ratio. Although 'aluminapowders as large'as 30 microns may be used, the alumina hour to a temperature of 1550 C.' The held at thistemperature for 2 hours.

.. The resulting 'sintered compact. had a compressive strength of -630,000 pounds-per square inch, a Rockwell A hardness rating of 92, and a Knoop hardness number of 1205. Its density was 3.44.

EXAMPLE II compact was The procedure of Example I was followed in forming hemispheres inch in diameter and solids x inch square and- A inch thick. The sintercd parts were ground these high pressures, it is not possible to achieve to the point of failure. As can be seen from the data of Examples I and II to cutting, tool tip properties using diamond grinding wheels. A A inch radius and a 3 to 9 degree'negative rake wercused on the squares.

Cutting test of these tool tips were carried out on an 18 inch long, six inch diameter bar of high carbon steel (AISI, grade D-3). The bar was turned at 240 revolutions per minute and'the tool, cutting iust below center,

was moved into the cut at 4 inches per-minute. The toolbit failed at a depth of 0.120 inch, and thisfailure was due to cocking and subsequent'chattering of the bar in the chuck. The surface my composition has a high compressive strength, is ex- .ceptionally hard, and is an excellent material for cutting tool tips.

t EXAMPLE 111* was about-400,000 pounds per square inch.

As can be seenby comparing the data of Examples I.

and III, the compressive strength ofarticles formed from my composition and by my preferred method have a compressive strength greatly in excess of-;that of pure A1 0 exposed by the cut was bright,

C. The compressive strength EXAMPLE 1V An article was made from pure alumina powder using the compression as well as the sintering step of Example I. The resulting article had a compressive strength of 571,000 pounds per square inch, which was considerably greater than the pure alumina, article of Example III,

but considerably less than that of my alumina-cobaltgold composition. Not only did this alumina article have a lower compression strength than 'my composition,

but it was quite brittle.

EXAMPLE i The procedure of Example I was followed in forming an article having the composition 95 percent Al O3-5 percent cobalt. The resulting article had a compressive strength of 532,000 poundsper square inch, considerably below that of the alumina-cobalt-gold composition; furthermore, the material was softer than my composition, having a Rockwell A hardness of 83.

EXAMPLE VI The procedure of-Examplel was followed in forming an article having the composition 95 percent Al O 4 percent cobalt, and 1 percent gold. Compression and cutting tests showed that this material was clearly inferior to the material of Example I.

EXAMPLE ,VII

EXAMPLES VIII-XII Cutting tests of other. tool materials were made in the same manner as the tests of my composition in Example [I.- The materials used .andfthe results, togetherwith :he results of. Example II, are given in the following by weight of a mixture of the metals cobalt and gold, wherein the weight of the gold is from 3 to 12 percent of the total weight of the metal components.

- 2. A composition of matter consisting essentially of 95 to 97 percent by weight alumina and 3 to 5 percent l by weight of a mixture of the metals cobalt and gold, wherein the weight of the gold is from 3 to 12 percent of the total weight of the metal components.

:able.

I Table Example Depth otCut No. lllatcrial at Failure (inch) 111,0. plus 3% (Jo-0.3% Au- 0.120 A1203 plus 2% CH0: 0. 040 A110 Hot Pressed (commercial grade). 0. 050

C A110,, Pure (hi-pressure pressed) 0. Ofill I W0 plus 10% Co 0.080

11 A110 plus 0.5% F020 0. 090

This table clearly shows the cutting superiority of 001 tips made from my composition.

The above examples are offered to-illustrate my invenion. ,Variations inthe composition and method of makng articles from the alumina-cobalt-gold powders will e apparent to' workers in the art, and my invention houldbe limited only in accordance with the following laims. i

Having thus described my invention, I claim: 1. A composition of matter consisting essentially of 0 to 97 percent by weight alumina and 3 to 20 percent 3. The composition of claim 2 wherein the weight-of the gold is about 10 percent of the weightof cobalt.

4. A composition of matter consisting of about 96.7 percent alumina, 3 percent'cobalt, and 0.3 percent gold.

5. A composition of matter consisting essentially of 80 to percent by weight alumina and 5 to 20 percent by weight-of a mixture of the metals cobalt and gold, wherein the weight of the gold is from 3 to 12 percent of the total weight of the metal components.

6. The composition of claim 5 wherein the weight of the gold is about 10 percent of the weight of cobalt.

7. A method of making an article comprising the steps of: d a

(a) mixing together alumina powder, cobalt powder, and gold powder in the amounts of 80 to 97 percent by weight alumina and.'3 to 20 percent by weight of a mixture of the metals cobalt andgold wherein the weight 'of the gold is from 3 to 12 percent of the total weight of the metal components;

'(b) pressing the resulting mixed powders at a pressure of at least about 100,000 pounds per square inch to obtain a formed article;

(c) sintering the resulting formed article.

8. The method of claim'7 wherein the mixed powders are pressed at a pressure of 125,000 to 200,000 pounds per square inch and the resulting formed article is sintered at 1450" C. to 1550 C.

9. Themethod ofvclaim 7 wherein the powder mixture consists of95 to 97 percent by weight alumina and 3 to 5 percent by weight of a mixture of the metals cobalt and gold, wherein the weight of gold is about 10 percent of the weight of cobalt. I

10. The method of claim 7 wherein the powder mixture consists of 80 to 95 percentby weight alumina and 5 to 20 percent by weight of cobalt and gold, and the weight of gold is about 10 percent of the weight of the cobalt.

Ryshkewitch: Oxide Ceramics, Academic Press, New York, 1960, page 422.

References Cited by the Applicant American Ceramic Society Bulletin 35, pp. 66-70 (1956), Feb. 15, An Oxidation Study of Cobalt-Alumina Mixtures.

CARL D. QUARFORTH, Primary Examiner. 

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF 80 TO 97 PERCENT BY WEIGHT ALUMINA AND 3 TO 20 PERCENT BY WEIGHT OF A MIXTURE OF THE METALS COBALT AND GOLD, WHEREIN THE WEIGHT OF THE GOLD IS FROM 3 TO 12 PERCENT OF THE TOTAL WEIGHT OF THE METAL COMPONENTS.
 7. A METHOD OF MAKING AN ARTICLE COMPRISING THE STEPS OF: (A) MIXING TOGETHER ALUMINA POWDER, COBALT POWDER, AND GOLD POWDER IN THE AMOUNTS OF 80 TO 97 PERCENT BY WEIGHT ALUMINA AND 3 TO 20 PERCENT BY WEIGHT OF A MIXTURE OF THE METALS COBALT AND GOLD WHEREIN THE WEIGHT OF THE GOLD IS FROM 3 TO 12 PERCENT OF THE TOTAL WEIGHT OF THE METAL COMPONENTS; (B) PRESSING THE RESULTING MIXED POWDERS AT A PRESSURE OF AT LEAST ABOUT 100,000 POUNDS PER SQUARE INCH TO OBTAIN A FORMED ARTICLE; (C) SINTERING THE RESULTING FORMED ARTICLE. 